This invention relates to a matrix for a catalytic reactor for exhaust gas purification, preferably for use in internal combustion engines and power plants. The matrix is made of corrugated steel sheet in long lengths or strips. The steel is coated with catalyst material. The corrugated steel is arranged in multiple-layers in a tubular housing through which an axial flow of exhaust gas passes parallel to the boundary surfaces of the layers.
German Offenlegungsschrift (OS) No. 2,733,640 shows a matrix wherein the steel strips utilized for matrix construction are made of two layers which include one flat strip and a corrugated strip. This OS also shows a matrix formed of corrugated steel bands that are wound into the desired shape and secured in the axial direction by tang-like punched out portions of one layer pressed into corresponding openings of the adjacent layer. German Unexamined, Published Patent Application No. 2,902,779 shows the use of flat steel strips and corrugated metal sheets in matrix construction to increase the turbulence of the flow passing through the matrix. The strips of corrugated metal sheet are applied to the flat steel strips, or, alternatively, individual flat strips are applied to the corrugated metal sheet. However, all of these arrangements suffer from a common drawback in that the manufacture of a matrix by these techniques is relatively expensive, especially if individual steel strips are used. A disadvantage of conventional types of matrix construction is that a radial equalization of the exhaust gases flowing through the matrix and the reactor is difficult, if not impossible, to attain even if the steel strips of the aforementioned type are provided with cutouts.
Accordingly, an object of the present invention is to provide a matrix for a catalytic reactor which is inexpensive to manufacture and which can be constructed in a variety of external shapes.
Another object of the present invention is to provide a matrix for a catalytic reactor which has an improved radial equalization of the flow profile of the exhaust gases moving through the reactor.
These objects are attained in a matrix formed from a single corrugated sheet which is folded in a meandering, serpentine-like pattern to form a plurality of layers, which matrix is subsequently arranged in a tubular reactor housing and traversed by an axial flow of exhaust gases. By means of this structure, the individual layers of the steel sheet can be formed in a relatively simple fashion, and they remain open on at least one side due to the manufacturing process. Consequently, and in contrast to a wound matrix where flow equalization is possible only in the peripheral direction even when individual strips are employed, the matrix of the present invention provides cutouts in the corrugated and flat strips for radial distribution of the exhaust gases, resulting in a more uniform flow profile and better turbulence of the gas flow and catalytic conversion. Therefore, even the outer layers of the catalyst material are exposed to the gases and contribute to the reaction process. Thus, the matrix can be utilized more advantageously.
A very simple arrangement of the matrix of this invention is obtained by folding the individual layers in a zigzag pattern. If the layers have unequal lengths in the folding direction, oval or round matrix inserts are produced without requiring a complicated structure of several parts. If the layers have equal length in the folding direction, rectangular or rhombic matrix inserts are produced so that the catalytic reactor serving for exhaust gas purification can be adapted in shape to the space available beneath an automobile.
To simplify the manufacturing process, the sheets utilized for forming the matrix are provided with preweakened buckling zones at the folding sites by, for example, perforations in the sheet material. Thus, production of a matrix according to this invention wherein the individual layers are folded over, for example, in a zigzag pattern, can be achieved in the same manner as an endless length of computer paper is folded after exiting from a printer when it is dropped vertically into a chute or other paper receiving apparatus. The perforations provided in the paper cause it to buckle slightly along the folding sites and thereby fold over into the desired shape. Similarly, a matrix can be formed by guiding a continuous perforated sheet or strip into a chute and folding it in the desired pattern. The thus-formed matrix can subsequently be inserted, for example, in a bipartite housing which compresses the matrix structure and adapts it for mounting in the axial flowpath of the gases. It is also possible to axially insert the matrix into a closed, tubular housing through apparatus which resembles a funnel.
The strip of sheet steel utilized for manufacturing the matrix can be formed by three layers wherein the two outer layers are relatively flat and may be provided with cutouts, and wherein the middle layer is a corrugated sheet which likewise may have cutouts or interruptions. However, it is simpler to use a single corrugated sheet, the corrugations of which exhibit a triangular cross section with straight walls lying, respectively, along the outer sides. These walls are separated on one end by gaps which extend transversely across the sheet. The width of these gaps as measured along the length of the sheet, however, is smaller than the width of the opposite, externally located walls (i.e., the third wall of the triangular corrugation). Such a corrugated sheet has the advantage that the individual folded layers do not fold into one another and, thus, folding is possible without the use of flat strips. These corrugated sheets are provided with cutouts so that radial equalization of gas flow is possible in the transverse as well as in the lateral directions. In this connection, the flow cross-section of all cutouts is suitably chosen so that a proportion of 5% up to 30% of the boundary surfaces adjoining each other in the individual layers is obtained. The cutouts should be optimally arranged so that good radial equalization is achieved without the loss of active surface area exerting a negative influence. The cutouts should also be distributed uniformly over the area of the boundary surfaces so that the aforementioned effect of good radial equalization of the exhaust gas flow with a uniform flow profile is attained.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment constructed in accordance with the present invention.